At a typical refueling station, fuel is pumped from an underground storage tank through a fuel dispenser, a hose and associated nozzle to the vehicle fuel tank. As the fuel enters the vehicle fuel tank, hydrocarbon vapors from inside the tank are exhausted or forced out of the tank. Environmental laws and/or regulations may require that vapors emitted from the vehicle fuel tank during refueling be captured and returned to the underground fuel storage tank. The captured vapor is returned through the vapor path of the nozzle, hose, dispenser and underground piping system back to the ullage space of the underground fuel storage tank. Balanced refilling systems are configured such that vapor forced out a vehicle tank is moved toward the storage tank by the pressure of fluid flowing into the vehicle tank.
An increasing number of vehicles include an onboard refueling vapor recovery (“ORVR”) system configured to capture/reclaim the vapor that would otherwise be emitted from the fuel tank during refueling. The ORVR system routes or feeds the vapor to a capture canister which includes activated carbon. When the refueling process is complete and the vehicle engine is running, vapor in the capture canister is fed to the engine where the vapors are burned during the combustion process.
A liquid seal ORVR system (the most common ORVR system) is typically designed such that the vehicle fill pipe leading to the vehicle fuel tank has a progressively reduced inner diameter. This configuration ensures that fuel flowing into the fill pipe covers or extends continuously across the cross section of the fill pipe during refueling to form a liquid seal, which prevents fuel vapor from escaping through the fill pipe. The reduction in diameter of the fill pipe also causes a vacuum to be generated during refueling due to the venturi effect. The phenomenon, known as an injector effect, draws surrounding air/vapor into the fuel flow stream, and creates a positive pressure in the vehicle fuel tank that forces the vapors into the vapor capture canister carried on the vehicle. However, a vehicle equipped with an ORVR system (i.e. an ORVR vehicle) can create a negative pressure in the nozzle, which can interfere with the proper operation of the nozzle/refueling system.